Aleph30 (and other Class-A amps) Hi-Lo Power Switch? - diyAudio
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Old 17th March 2006, 03:27 AM   #1
Daveis is offline Daveis  United States
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Default Aleph30 (and other Class-A amps) Hi-Lo Power Switch?

I'm currently thinking of getting several commerically built Aleph-30's to power my linearray system. The problem is that with 4-5 of them they'd be putting out 1000 watts or more. At 1000 watts it's like having a little space-heater running full-tilt. While this is great in Iowa during the winter, what do I do in the summer?

Any ideas on how I could derate my Aleph-30's to run at say 10-15 watts/channel. Then in the winter or when I want to rock out crank them up?

I'm thinking a variac might do the trick, but what's the limitations on using one?
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Old 17th March 2006, 06:57 PM   #2
Buhl is offline Buhl  Denmark
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I was fooling with the idea some time ago, thinking of adding a relay changing between two biasresistors in my Zen4 - but dropped it, because basically I think that it is stupid robbing class a amps what the are good at - they sound good with high bias - if you try to run them into class B land - why not go all the way, and build a box full of gainclones - they sound really, really good, and I have got some awsome bass out of them, paralleling two 3875 pr. channel, and using a comibnation of big and small electrolytics - in many aspects, I like this type of amp over my zen 4 - especially when using low impedance loads. The Gain Clones have very low bias current, and thus will not heat your room by more than a fraction of a degree

Cheers !
Hans - from Denmark, where the weather has gone crazy, making me wish I had finished some more class A amps....
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Old 19th March 2006, 04:58 AM   #3
Daveis is offline Daveis  United States
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Default But what if you dont need 30-watts?

Ok, I agree that Class-A still sounds best. But what if you only NEED about 10-watts Class A most of the time. Maybe your speakers are efficent or you dont need to play loud most of the time.. And you can get some good deals on some already built Aleph 30's?

(I've currently got several TI Equibit digital amps and they just arent cutting it sonically.)
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Old 19th March 2006, 02:13 PM   #4
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If it's 10W Alephs you're wanting, build a gang of Mini-As.

Grey
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Old 19th March 2006, 02:34 PM   #5
moe29 is online now moe29  United States
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for the few hours a day you are listening... just crank down the air conditioner!
(the addition of a cool beverage may help too)

Sometimes one has to be brave to bask in the glow of Class A goodness
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Old 20th March 2006, 03:24 AM   #6
Daveis is offline Daveis  United States
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Default mini-a's as good?

Are the mini-a's as good sounding within their power range as Aleph-30's?

Is their a best mini-a variation?

I'm still thinking someone (Nelson?) knows how to best limit the power of an Aleph 30. I thought I heard him saying that a variac could limit power and was also useful for initial testing of an amp.
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Old 20th March 2006, 08:30 AM   #7
Noise is offline Noise  Denmark
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I think a Variac would work, but if you want to use so many amps, you need a really big Variac. They can be very expensive, if i'am not wrong.

I think the best solution would be, to build a "Power down" circuit in to all the amps. You have to find the resistor(s) that set the bias current for the outputstage and replace it with a higher value resistor. That will set the bias to a lower value, to go back to normal bias, you then add a switch/relay and another resistor in parrallel with the first one. (The value of both resistors have to be equal to the original bias-resistor). Now you should be able to simply "flip a switch" to change the amount of bias and heat production. (You should turn the amps off before operating the switch to avoid noise and destruction of parts).

Since I don't know the A30 amps my self, I can't tell you exactly how to do it, but I have seen the circuit described above, used in other class A amps with power down function.

Hope I could help!
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Old 20th March 2006, 07:03 PM   #8
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The problems you have to deal with are mostly offset and thumps.

Refering to the A30 schematic, you can set the amplifier to bias
at a lower level by switching the values of R19 and R14. If you
just switch R19, you will get offset, which may not be much of a
problem if the amp is capacitively coupled in the feedback loop
and you can put up with the transient noise.

If the offset and transient are an issue, then turn the amp off
and switch the values.

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Old 24th March 2006, 03:38 AM   #9
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I don't know how much this will help....

Connect 2 identical amps in series. this way u will lead to half the DC supply in case u don't have regulated power. If it works ok, make a permanent switch arrangement.
The voltage sharing will not be very good.

Gajanan phadte
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Old 24th March 2006, 09:52 AM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by gmphadte
I don't know how much this will help....

Connect 2 identical amps in series. this way u will lead to half the DC supply in case u don't have regulated power. If it works ok, make a permanent switch arrangement.
The voltage sharing will not be very good.

Gajanan phadte

with just half voltage in + rail , CCS for input LTP will go mad


NP sez enough; at least from practical point of view
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